This application claims priority from Canadian Patent Application No. 2,242,497.
The present invention relates to a method and apparatus for the continuous performance monitoring of a lead acid battery system, and more particularly to such a method and apparatus which is easier to install and implement and provides added flexibility.
Lead acid batteries are a commonly used source of electrical energy in the case when a main source, typically an AC supply line, fails. Typically, a bank of batteries will be interconnected in a system configuration to provide the desired voltage and power for short term emergency situations, until the AC supply line is re-established or until a generator can provide the necessary power requirements. Such systems are often used as back-ups for hospital equipment, telecommunications equipment, computer equipment, etc.
However, battery systems represent what has been termed a bullet approach, i.e. their performance is only truly evaluated when they are in use. This is a considerable inconvenience, since the reliability of the entire system is dependent on each of the batteries. Should the battery system fail, this can lead to considerable monetary loss, and considerable loss of service with critical consequences, particularly in the case of hospital equipment and telecommunications systems.
There are a number of symptoms which can be indicative of a failed battery. Some of these symptoms can lead to entire system failure and the requirement for premature (and costly) replacement. One condition in particular can create a dangerous situation for persons servicing the system or bystanders: thermal runaway. Thermal runaway is a critical condition arising during constant voltage charging in which the current and the internal temperature of a battery produce a cumulative mutually reinforcing effect which further increases them and can lead to the destruction of the battery.
There are a number of systems and devices on the market which provide either off-line monitoring or in service test. Depending on the price and complexity level, each of these systems provide a more or less comprehensive evaluation of system performance. However, the present systems represent a relatively complex installation process and do not, according to the Applicant, provide continuous performance monitoring.
As an example of the present systems and the parameters which are monitored, reference may be made to the following U.S. Pat. Nos. 4,707,795; 5,546,003; 4,916,438; 4,217,645; 5,206,578.
These systems generally provide sensing means at each battery, connecting each sensing means to a remote monitor through analog communication means such as a pair of copper wires and sensing a variety of parameters for each battery. The remote monitor or the sensing means directly perform calculations to extract from the sensed parameters values for indicia such as battery voltage, battery temperature, system voltage, ambient temperature, float current, AC component of the battery voltage, AC current component, etc. However, each of these systems describes a complex installation process, and the installation of some of these systems may require taking the battery system off-line during set-up which users do not appreciate.
It is also known in the art to measure a variety of parameters while charging, discharging, loading or using the battery system.
One of the parameters which can be useful to measure is the battery impedance to provide an indication of the condition of the battery. Typically, in order to measure the impedance, a current is imposed on the battery and the resulting voltage measured in order to calculate the impedance since both voltage and current are known. One such system for measuring the impedance of a plurality of batteries (not each individual battery) is described in U.S. Pat. No. 5,281,920. The system of this patent divides each string of batteries into two and applies the current only to one half of the string. The disadvantage with this system is that it is cumbersome to install, and the voltage that is measured is done so for the totality of the half-string, not for each individual battery and so is the resulting value for the impedance.
Accordingly, it is desirable to continuously monitor a battery system to provide adequate information in order to evaluate the performance of the system and to perform preventive maintenance on the system.
It is an object of the invention to provide an interface device which provides adequate information between at least a portion of a string of batteries serially connected and which can be easily installed with a minimum of manipulation.
In accordance with the invention, this object is achieved with an interface device for interfacing at least a portion of at least one string of batteries with a battery monitoring system. The interface device includes at least one probe means for respectively probing the portion of the at least one string, each of probe means including a controllable sensing means for sensing a plurality of parameters of the corresponding portion, a communication means for communicating data to and from the controllable sensing means, the data including control signals sent from the battery monitoring system to the controllable sensing means, and information signals relating to the parameters of the corresponding portion that are selected by the control signals; and a memory for memorizing an address assigned to the corresponding probe means upon reception of an initialization signal sent by the battery monitoring system via the communication means. The interface device further includes a bus for serially interconnecting the communication means of each of the at least one probe means to the battery monitoring system in a daisy chain manner.
The invention is also concerned with a battery monitoring system comprising a plurality of interface devices and a system server.
It is another object of the invention to provide a battery monitoring system which accurately and easily measures the battery impedance for each battery in a string of batteries. A corollary object of the invention is to provide a method for measuring the battery impedance of a plurality of batteries serially connected to form at least one string of batteries.
In accordance with the invention, this other object is achieved with a plurality of batteries connected in series to form at least one string of batteries; a plurality of probe means for respectively probing at least a portion of the at least one string, each of the probe means including: a controllable sensing means for sensing a plurality of parameters of the corresponding portion; a communication means for communicating data to and from the controllable sensing means, the data including control signals and information signals relating to the parameters of the corresponding portion that are selected by the control signal; a bus for serially interconnecting the communication means of each of said at least one probe means in a daisy chain manner.
The battery monitoring system also includes a current injection means connected to the at least one string for injecting a current in the at least one string upon receipt of a control signal. The system is further provided with a system server connected to the bus and configured to select one of the probe means, to transmit control signals to a selected one of the probe means and to receive information signals relating to the characteristics of the corresponding portion, memory means for storing the information signals, calculating means for calculating a plurality of values relating to the characteristics and alarm means for raising an alarm when one or more of the values is outside a predetermined range. The system server is operatively connected to the current injection means for sending a control signal to the current injection means to inject a current in said at least one string.
The invention further provides for a method for initializing each probe in a battery monitoring system, and a method for measuring the internal impedance of a battery within a string of batteries.